1. Field
Embodiments described herein relate generally to a channel estimator in a broadcasting reception system and a wireless communication reception system.
2. Description of the Related Art
In a broadcasting system and a wireless communication system, in general, a wireless signal transmitted from a transmission station is reflected, scattered, and diffracted by geographic features, buildings, and other objects before reaching a receiver, and the resultant plurality of wireless signals reach the receiver. When the receiver receives the wireless signals having originated from the single transmitter but traveled through different paths, the signals are combined into a single signal having a deformed waveform in some cases. The phenomenon is generally called multipath, and the paths through which the wireless signals travel are called multipath channels.
To address the problem, the receiver processes the received signal having a distorted waveform to reproduce the original waveform of the wireless signal transmitted from the transmission station. The process is generally called an equalization process.
In general, a distortion component produced in each multipath channel can be expressed as a filter response obtained when an impulse signal is inputted, and the equalization process performed in the receiver is improved by precisely estimating the channel response. The channel response is generally called a delay profile.
It has been known that a channel estimator in a receiver in a wireless communication system uses a known signal sequence contained in a received signal as a reference signal and determines complex time correlation between the received signal and the reference signal to calculate a delay profile.
In some wireless systems, a specific code sequence (a pseudo random noise (PN) sequence, for example) is used as the known signal sequence and cyclically extended prefix and postfix are inserted before and after the specific code sequence in some cases.
Now, for example, assume a wireless system in which a signal frame is composed of the known cyclically extended signal sequence described above (hereinafter referred to as a frame header) and signal data (hereinafter referred to as a frame body) and the thus configured signal frame is arranged. When the delay profile of the signal frame is calculated by using a channel estimator, the precision in the channel estimation is degraded by the following components:
(1) Degraded component produced by cross-correlation between the frame header and the reference signal
(2) Degraded component produced by cross-correlation between the frame body and the reference signal
The degraded component (1) is produced in principle when complex time correlation between the frame header and the reference signal is calculated.
The degraded component (2) is very problematic because the cross-correlation between the frame body and the reference signal increases when a multipath signal having a delay longer than the frame header length is received.
However, when a multipath component and a degraded component are distinguished from each other in the calculated complex time correlation, a multipath component having relatively high electric power can be readily identified, whereas a multipath component having relatively low electric power, if any, is difficult to be identified. To identify a multipath component having relatively low electric power, for example, a signal having electric power higher than or equal to a predetermined threshold value can be judged as a multipath component. In this case, however, a multipath component may not be detected when the threshold value is set at a high value, whereas a degraded component may be wrongly judged as a multipath component when the threshold value is set at a low value.